This invention relates to a method used for the production of atmospheric pressure plasmas of various gaseous mixtures and their usage for the surface modification of materials.
Atmospheric pressure plasmas have been known since the dawn of man. A classic example is lightning. These atmospheric plasmas (DC-type) occur when a high potential causes the dielectric breakdown of air ( greater than 8 KV/cm in air). This type of plasma is used for producing various types of ceramic coatings in an apparatus known in the industry as a xe2x80x9cplasma gunxe2x80x9d. Most other plasma producing devices do so in a vacuum system. Such vacuum-based systems are widely used in the microelectronics industry both for the deposition of thin films and for various etching and surface modification applications. Most of these vacuum-based plasma generating systems use RF or microwave energy excitation to sustain a stable plasma environment. Whereas a stable plasma is relatively easy to generate and maintain at low pressures it is much harder to do so at ambient pressures, due to the very short mean free paths and large recombination rate of the plasma radicals. Discussions of vacuum-type plasmas are given in xe2x80x9cHandbook of plasma processing technologyxe2x80x9d, edited by S. Rossnagel, J. Cuomo, and W. Westwood.
Whereas the capabilities of vacuum-type plasmas are limited by the size of the vacuum chamber and the associated pumping system, an atmospheric pressure plasma system can be configured with very little limitation on the size and shape of the objects treated. It can be made compact and portable as described in our co-pending U.S. application Ser. No. 08/572,390 filed Dec. 14, 1995, details of which are incorporated herein by reference. This system can also be scaled up with very little additional cost either through a large parallel plate configuration or through an array of small orifices, it can be installed in a variety of environments without any facilitation needs and its operating costs and maintenance requirements are minimal.
H. Koinuma et al., xe2x80x9cDevelopment and Application of a Microbeam Plasma Generatorxe2x80x9d Appl. Phys. Lett. vol. 60, p. 816-817, (1992) K. Inomata, xe2x80x9cOpen Air Deposition of SiO2 Film From a Cold Plasma Torch of Tetramethoxysilane-H2xe2x80x94Ar Systemxe2x80x9d Appl. Phys. Lett., vol. 64, p. 46-48 (1994)
The present invention relates to a device and a method for producing stable atmospheric pressure glow discharge plasmas using low power RF excitation applied through a tuner to a resonant LC circuit, said resonant circuit having as one of its components a discharge chamber capacitor through which a mixture of gases is passed. In addition, the discharge chamber can be configured so that a magnetic field is provided along the direction of the flowing gases such that it provides a force on the charged species in the plasma region thus increasing the ionization ratio. The magnetic field can be provided either through a set of permanent magnets or a coil attached on the external surface of the discharge chamber. These atmospheric pressure plasmas can be generated in various gases flowing through the discharge chamber, the typical case being a combination of a noble gas such as Helium or Argon and a reactive gas such as Oxygen or Nitrogen. The specific gases used and their respective percentages depend on type of surface modification processing sought such as etching of organic materials, surface modification of composites and polymers, and chemical interactions with surface layers of materials.
It is an object of this invention to provide a source for generating atmospheric pressure glow discharge plasmas which is simple and relatively inexpensive to construct.
Another object of this invention is to provide an atmospheric pressure glow discharge plasma source utilizing a resonant circuit and RF excitation to ionize the gas molecules without the need of a vacuum chamber or pumping systems.
Yet another object of this invention is to enhance the ionization rate of the molecules using a magnetic field extended parallel to the gas flow.
It is also an object of this invention that the ionized gases generated in the discharge chamber be used as a source of reactants for etching organic materials and in general modifying the surface characteristics of material.
These and other objects of the invention will be apparent from the following detailed description of preferred embodiment when read in connection with the appended drawings.